1. Field of the Invention
The present invention relates to an image handling system and more particularly to a variable image-magnifying apparatus and an image forming apparatus using a scanning type recording system.
2. Description of the Prior Art
FIG. 1 shows a main construction of one prior art recording apparatus. In the figure, a recording head 1 mounted upon a recording head carriage 2 is disposed to be movable on a main scanning guide rail 3 the direction of arrow A. The recording head carriage 2 is moved by a timing belt 4 driven with a drive source such as a pulse motor 5. The recording head 1 is provided with a plurality of nozzles 6 to which ink from an ink tank 7 is supplied, an input with a recording signal from a read-out device via a signal line 8 to thereby move in the main scanning direction while jetting out ink drops. The ink drops are recorded onto a recording paper 9 disposed facing the recording head 1. Numeral 10 represents a width capable of being printed out with a single main scanning. After completion of a single main scanning and return to the start position, a sub-scanning movement in the direction of arrow B, corresponding in amount to the print width 10, is effected by a drive source 11 such as a sub-scanning pulse motor. Succeedingly, the operation for the next main scanning is again repeated, thus printing out the whole image region.
In order to perform a variable magnification with the apparatus of this kind, generally a thinning system is used in a scale reduction mode in order to thin input pixel signals in accordance with a scale reduction ratio. In particular, assuming that 1 mm of the image is printed out by 8 dot/mm in an equal magnification mode, if the image is to be reduced by 1/2, every second dot of the 8 dot signal is thinned, that is, 4 dots are thinned, thereby obtaining a 0.5 mm image from a 1 mm image in equal magnification. Contrary to the above, in a scale magnification mode, e.g. a double-size mode, an interpolation system is used wherein two dots are printed out for each dot of the image signal in the equal magnification mode. Upon using such system, since the original image signal is thinned in the scale reduction mode, the amount of information is reduced and hence the printed image quality is signficantly deteriorated. Furthermore, in the scale reduction and magnification modes using the serial scan type apparatus such as shown in FIG. 1, since the image width varies with the magnification ratio at a time irrespective of the constant number of printing nozzles of the recording head, signal processing becomes very much complicated. In particular, it is assumed that the head 1 has 32 nozzles and hence the information amount corresponds to 32 dots in the equal magnification mode In a 1/2 scale reduction mode, the information amount is compressed to that corresponding to 16 nozzles in the head. Therefore, if all of the 32 nozzles are to be used, then the information amount becomes that corresponding to 64 dots as of the equal magnification mode. Alternatively, in the twice-size mode, the information amount in 32 dots of the equal magnification mode can not be sufficiently processed with the 32 nozzles of the head. That is, the output amount obtainable at one time with the 32 nozzles of the head corresponds to the information amount in 16 dots of the equal magnification mode. As above described, it is necessary to control the information amount capable of being output at one time for each scale reduction, equal magnification, and magnification mode. Thus, there arises a problem that the signal processing circuitry for such control becomes complicated.
One example of the structure of a prior art ink jet printer with a single color output is shown in FIGS. 2 and 3. Represented by numeral 101 is an ink jet nozzle made of glass tube about which a piezoelectric element 102 is engaged. The tip portion of the ink jet nozzle 101 is squeezed to form a nozzle 101a, while the end portion is coupled to one end of a tube 103. The other end of the tube 103 is immersed into ink 105 in a sub-ink tank 104. The lower end portion of the tube 103 is provided with a filter 106. On the upper side of the sub-ink tank 104, a lid 107 is fixedly mounted so that the sub-ink tank 104 as a whole is hermetically constructed. An air layer 104a having a predetermined space is formed within the sub-ink tank 104 at its upper portion.
A joint portion 108a of the sub-ink tank 104 is coupled to one end of a flexible tube 108, while the other end thereof is coupled to a not shown main ink tank. Another joint portion 109a is formed above the joint portion 108a connecting the flexible tube 108. The joint portion 109a is coupled to one end of a ink suction tube 109, while the other end thereof is coupled to a not shown negative pressure source.
The ink jet nozzle 101 and sub-ink tank 104 constructed as above are mounted on a not shown carriage and disposed facing a platen 110. The piezoelectric element 102 is compressed by energizing it in response to a control signal, thereby jetting out ink from the ink jet nozzle 101. Thus, a printing paper 11 fed in contact with the platen 110 can be printed out.
An example of printed dots obtained through the above operations is shown in FIG. 4(a). In the figure, the pitch l between the printed dots 112 is determined considering the relation between the energization frequency for the piezoelectric element 102 shown in FIGS. 2 and 3 and a feed speed (hereinafter called as main scanning speed) of the carriage mounting such as the jet nozzle 101. The dot diameter D of an ink drop is set for example as D=.sqroot.2l so as not to make any clearance between the printed dots as shown in the dot disposal of FIG. 4(a). After completion of printing out the first line, the platen 110 shown in FIGS. 2 and 3 rotates to feed the recording paper 111 disposed between the platen 110 and the ink jet nozzle 101 by the distance in the direction perpendicular to the main scanning direction (hereinafter called as sub-scanning direction). The above operations are repeated to print out the overall image area on the recording paper 111. In this case, by varying the main scanning speed and the feed amount of the sub-scanning direction, the scale reduction and magnification of an image can be attained. However, in some cases, there arise problems as shown in FIGS. 4(b) and 4(c). It is assumed here that the pitch between dots in the scale reduction and magnification modes is l' and l", respectively. In the scale reduction mode, the dot density becomes high as shown in FIG. 4(b) so that the superposed area between dots becomes large. As a result, in some cases, the printed image becomes dirty and the original image is not reproduced faithfully in quality due to the same, large dot size. Contrary to the above, in the magnification mode, the disposal of dots becomes coarse as shown in FIG. 4(c) so that a clearance m between dots exists to thereby expose the surface of a recording paper. Therefore, in many cases, disadvantages are brought about that not only the overall density is degraded but also the original image can not be magnified with fidelity. Thus, problems still may exist if the main scanning speed and the feed amount of the sub-scanning are merely varied.
Apart from the above, in obtaining a copy of an image, generally there are two considerations; one being to copy the original quickly even if the image quality is somewhat deteriorated, and the other being to copy the original so as to obtain a good image quality irrespective of its copying speed. Furthermore, documents made of alphabetical characters for example are satisfactory even if a high quality image is not incorporated for printing the documents. However, in the case of a photographic image, if a recording apparatus of the type printing out only two logical values is used, it is necessary to employ a dither process for regenerating a half tone. In this case, because of a dither matrix, pixels for a half tone printing become coarse. In order to compensate the coarseness, it is necessary to prepare high density print dots. Although relatively coarse pixels are sufficient for usual handwriting characters, in the case of typeprinting with many thin characters, if coarse pixels are used, the recording results are hard to read. Thus, in many cases, a high density recording is required.